Went out today in search of reloading supplies, and decided to run up there from Chino Hills.
First mistake was going right at the fork, into a prison? Opps
Next was getting peppered pulling into the lot? Hmm
While sitting there waiting for the reloading shop to open, I see a line around 20-25 deep just to get in the registration shack.
Also, while waiting, I notice the whole parking lot is getting peppered with birdshot, most noticeably a new Range Rover and Mercedes SUV.
Go in and make my purchase, come out and there is a AR that doesn't look all that Ca. compliant being waved around and an argument on the rifle? range.
Wholly crap, is it always that crazy here?
Shot 5 stand at Prado, and it was nothing like this zoo.
Kind of a culture shock for this bumpkin cheese head.

Ok, cool!
Only things I brought out are a .243 700, and a 642, didn't know if anything else was legal(shock waves excluded)

OP, yours is a common misconception amongst many people.  

Here in California, you can legally have and use a properly configured AR in all its "assault weapon" glory accompanied by bazillions of "high capacity" magazines.  No one should be surprised by their presence, especially so at a shooting range.  It can still be compliant because of the most invisible of features, a piece of paper kept with the rifle in its gun case.  

Were an owner/user challenged regarding the legality, they should first ask for identification confirming the status as LEO.  If they are, you have to decide how you want to handle the situation.  Producing a copy of the assault weapon registration form is one option.  <-- I have never once been challenged by anyone.

If the questioner is not a LEO, they should be reminded to mind their own business and then you walk away.

Why were they arguing?  Who knows, who cares?

@Trollslayer,
I don't know, and could give 2 shits, like I said I'm from Wi.
I was just there to buy some reloading componants, but the whole set up seemed kind of hape hazard.
Peppering vehichles in a parking lot dosen't seem all well...
If you guys enjoy it, more power to you.
Not meaning to piss in anyones Wheaties, just a casual observation.

By "peppering" so you mean birdshot raining down on the parking lot?  If so, yeah, that's not cool, a real liability for the range.

I'm not sure I've ever even been there, maybe once, a long time ago.  Enjoy it, HELL NO!  I'd have probably left.

Yes birdshot, probably from the 5 stand range, up on the hill.
While there(20 minutes), I heard about 4 "wingers" richocettes...
You all can have it, I've been shot twice and stabbed once.
It sounded like wedding night(Thursday) in Iraq

I thought that place burned down

I used to work next to a range in Corona and we had three pistol rounds penetrate the windshield of a customer whose car was parked in our lot and end up embedded in his car seat.  I was told it was not the first time something like that had happened.  There was a fatality there a couple of years ago, IIRC, due to an unsafe range layout.  Place was stupid expensive to shoot at and didn't even have very good facilities.

I'm really not that fond of going to the range, especially public ones.  BLM land is just so much better, especially if you have a spot that doesn't get the heavy traffic that the popular BLM spots do.  Most days I go I'm likely to be the only person I see (besides anyone who comes with me or meets me there) the whole day, and I can shoot to several hundred meters, unlike most public ranges out here.